This invention relates to microform viewers and more particularly concerns a viewer having improved film handling and image projection.
Microform viewers, for use with microfiche, roll film, film strip, aperture cards and the like, generally comprise a source of illumination, a film transport for positioning the film relative to the illumination source, a screen, and a lens system for projecting an image of the illuminated film upon the screen. Prior viewers, particularly those of a sufficiently small size for easy portability, have suffered from a number of inconveniences and deficiencies in operation. For example, although motion of the film in one direction is controlled by turning a knob, a second direction of shifting of the film has required a lateral shifting of a control. For a small lightweight viewer, this shifting mode may require use of two hands--one to move the transporter control and the other to hold the viewer case--in making this adjustment. This adjustment is thus difficult and at best inconvenient since the operator who may be making a sales presentation or taking notes of the display generally has but one hand conveniently available for operation of the viewer.
Glass flats that maintain position of the film in the focal plane of the projecting lens have not been readily accessible heretofore for cleaning. In various prior art arrangements, either the outside surfaces or the inside surfaces have been accessible. However, access to both outer and inner surfaces has not been readily available in prior machines, nor have such machines been able to accept microforms of different thicknesses.
Where dual lenses have been employed in the past, these could be changed or shifted to and from operating position only by manipulating elements within the viewer case and could not be shifted from the outside. Further, no simple procedure for focusing one or the other of a pair of projecting lenses was previously available. Dual lenses are employed because different microforms having different size and spacing of images require different magnifications. If indexing is employed it should be capable of handling more than one size and spacing of the film images.
These and other problems of prior viewers significantly detract from their convenience, utility and desirability. Accordingly, it is an object of the present invention to provide a microform viewer that eliminates or minimizes above-described disadvantages.